Organometallic derivatives of transition metals are finding increasing use in numerous applications, particularly as additives in fuels and petroleum products, yet the biological properties of this class of compounds are virtually unknown. We propose a systematic investigation of the toxicity, pharmacological properties, and metabolism of a set of organometallic compounds of chromium, manganese, and iron. The compounds to be studied are analogs of simple organic compounds whose toxicity, pharmacology, and metabolism are very well known (e.g. benzene, toluene, styrene; amphetamine, ephedrine, diphenhydramine). The analogy is simply based upon replacement of a phenyl group by an aromatic organometallic equivalent such as (C5H5)FeC5H4-, (CO)3CrC6H5-, or (CO)3MnC5H4-. Both acute and "prolonged" toxicity will be evaluated using histological as well as biochemical techniques. Pharmacological studies as well as metabolism studies will be performed in vivo as well as in vitro, and any metabolites with an intact organometallic moiety will be isolated and fully characterized.